Gas plasma panels having an inherent memory were originally disclosed in U.S. Pat. Nos. 3,499,167--Baker et al and 3,599,190--Bitzer et al. These panels have several inherent advantages over the cathode ray tube display and are presently used commercially, principally as digital data read-out devices. A problem associated with the state of the art technology is that the drive and control circuitry for the panel has been trouble prone and expensive in view of the number of circuits required and the complexity of these circuits.
One of the reasons for the circuit complexity has been the nature of the panel itself. Basically, the panel consists of two glass plates with a gas mixture sealed between them. A plurality of X-axis electrodes are deposited on the interior substrate of one plate and a plurality of Y-axis electrodes are deposited on the interior of the other plate, thereby providing a plurality of intersecting X and Y electrodes. A voltage of between 200 and 250 volts is required to discharge the gas between intersecting electrodes to emit light at this point. A lesser alternating current voltage will sustain the gas in the light emitting state, such that the gas will emit a pulse of light at each transition of the applied AC waveform. A precisely timed, shaped and phased multiple level alternating voltage waveform is required to control the generation, sustaining and erasure of light emitting gas discharges at the selected locations on the plasma display panel.
Typically in the prior art systems, a multiple level alternating voltage sustainer drive signal is applied to both the X and Y electrodes, so as to present a composite sustainer waveform across the gas at each point or cell in the display panel where the X and Y electrodes intersect. As a result, each of the X and Y electrodes are required to be driven by a complex sustainer circuit. Moreover, not only is a sustainer circuit required for both the X and Y set of electrodes, but in addition, a plurality of digital logic elements are required to generate a plurality of timed pulse trains for controlling the on and off intervals of the transistors within each of the X and Y sustainer circuits.
Another disadvantage of the prior art sustainer drive circuits is that they commonly utilize inductances and transformers as energy storage elements and isolation devices. These are ordinarily high-cost items, resulting in a further increase in the cost of manufacture of the overall system. In addition, it has been difficult to make the prior art circuits reliable. Thus, for example, the stray inductances associated with the panel tends to result in deleterious ringing of the output drive transistors of the sustainer circuits.